INT 10,C - Write Graphics Pixel at Coordinate

	AH = 0C
	AL = color value (XOR'ED with current pixel if bit 7=1)
	BH = page number, see VIDEO PAGES
	CX = column number (zero based)
	DX = row number (zero based)

	returns nothing

	- if bit 7 is 1, color specified is XOR'ed with current pixel
	- page number in BH ignored for 320x200 4 color graphics mode
	- this function is known to destroy AX and possibly SI and DI on
	  on some PS/2 VGA systems